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cisco ccna free course.generates a longer digital signature of 160 bits. Of the two functions, SHA.1 is more secure, but also slower.In IPSec, the HMAC function is used to confirm that the packet comes from a trusted source device (packet authentication) and has not been tampered with (packet integrity). The source device runs the HMAC function with the packet to be sent and a symmetric key to generate a digital signature. Then, the digital signature is added to the packet and sent to the target device. The target device repeats the above process: the original packet and the symmetric key are taken as input. The generated digital signature should be identical to the signature in the packet; if it is, the sender of the packet knows the symmetric key and it has not been tampered with; otherwise, the packet is discarded because either the digital signature is forged or the packet was tampered with during transmission from the source device to the target device.Authentication: verifying the peerIn any VPN solution, including IPSec, verifying the identity of the peer using some authentication method is an important component. IPSec supports two types of authentication: device and user (often referred to as extended authentication, abbreviated as XAUTH.) L2L sessions support only device authentication, while remote access sessions support both types of authentication. Device authentication supports two peer authentication methods.. Pre-Shared Key (PSK): PSK requires a pre-shared symmetric key to be configured on each VPN peer. This key and the peer's identity information will be used to generate a signature. and the remote end will use the same PSK to verify the signature.. RSA Signatures: RSA signatures use asymmetric keys to verify identities. The signature hash generated using the private key is placed in the certificate issuing authority(CA) generated digital certificate and the signature is verified using the corresponding public key. Of the two authentication methods, PSK is easier to implement, but the scalability of certificates signed using RSA is much higher.IPSec ProtocolIPSec is actually a set of standards, protocols, and technologies that work in concert to establish a secure session (often referred to as a tunnel) to a remote peer. An IPSec tunnel contains three connections: a management connection and two unidirectional data connections. The tunnel establishment process consists of two phases; the management connection is established in the first phase and is used to share IPSec-related information between the two peers. The two data connections are established in the second phase and are used to transport user traffic. All three connections are protected. The following briefly describes the protocols used to establish the tunnel..ISAKMP: Internet Security Association and Key Management Protocol is used to establish and maintain the tunnel. it defines the format of the management load. specifies the encryption algorithm and the key exchange protocol used by the HMAC function. negotiates how to establish the tunnel between the two devices. and authenticates the remote device.